Low-melting-point substances, for example, wax-like substances, glycerine esters of fatty acids, etc., are used in fields such as sustained-release preparations and preparations for masking bitterness.
For example, Japanese Unexamined Patent Publication No. 1995-76517 discloses a pharmaceutical preparation obtained by coating very small spherical particles produced by melting or dispersing a pharmacologically active substance that has an unpleasant taste in a molten wax-like substance, with a coating film formed from a hydrophobic substance and/or a water-insoluble polymer.
The above-mentioned publication only discloses pH dependent water-insoluble polymers such as the polymers soluble in gastric juice or enteric polymers, but nowhere discloses a pH-independent water-insoluble polymer. Furthermore, because the invention disclosed in the above-mentioned publication uses organic solvents to dissolve the water-insoluble polymer, it causes problems of adverse effects on workers' health, environmental pollution, residues in preparation, etc.
Japanese Unexamined Patent Publication No. 1996-143450 discloses a sustained-release preparation comprising a water-soluble pharmacologically active substance, a glycerine ester of a fatty acid and a water-insoluble substance. The sustained-release preparation is obtained by mixing a water-soluble pharmacologically active substance with a glycerine ester of a fatty acid, melting and granulating the mixture, adding a water-insoluble substance to the granulated substance, regranulating, and compressing the regranulated substance.
However, pharmaceutical preparations that use low-melting-point substances, such as wax-like substances, glycerine esters of fatty acids, etc., have the drawbacks of having low long-term stability and lowered release rate of pharmacologically active substances from pharmaceutical preparations that have been stored for a long time.
The above-described two publications nowhere disclose the release rate of pharmacologically active substance after preserving the pharmaceutical preparation over a long period of time.